From Wikipedia on the HeathKit.
By the 1980s, the continuation of the integration trend (printed circuit boards, integrated circuits, etc), and mass production of electronics (perhaps especially computers overseas and in plug in modules) eroded the basic Heathkit business model. Assembling a kit might still be fun, but it could no longer save much money. The switch tosurface mount components and LSI ICs finally made it impossible for the home assembler to construct an electronic device for significantly less money than assembly line factory products. As sales of its kits dwindled during the decade, Heath relied on its training materials and a new venture in home automation and lighting products to stay afloat. ...
On March 30, 1992, the end came. Heath announced that it was closing out its kits and leaving the business after 45 years, an event important enough to a number of people that it was reported on the front page of the New York Times.